Time difference of arrival (TDOA) is a well known method of locating a transmitter having an unknown location. In a time difference of arrival system, a transmitter can be located on a hyperboloid by knowing the locations of two receiving stations and the difference in the arrival time of the signal at the two receiving stations. The absolute time the signal was transmitted is not needed.
Typically, the receiving station has TDOA circuitry necessary to geolocate a transmitter, which increases the cost operations and is prone to failures at each receiving station.
U.S. Pat. No. 5,191,342 entitled “FIX-TRACKING SYSTEM” discloses a method to determine the location of a transmitter by using the time difference of arrival method and a communications link (telephone line) to communicate received signals to a central, or control station. The method disclosed in U.S. Pat. No. 5,191,342 does not compensate for the error introduced from the time delay of the communications link as the present invention does. U.S. Pat. No. 5,191,342 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,859,613 entitled “SYSTEM AND METHOD FOR GEOLOCATING PLURAL REMOTE TRANSMITTERS,” discloses a method of having a plurality of transmitters send a beacon signal to a receiving station at a predetermined time, which may be identified using a geosynchronous satellite. The location of the transmitter is calculated at each receiving station using a TDOA method that is known in the art and the results are transmitted to a central control station over a telephone link. The present invention does not require TDOA circuitry at the receiving stations, as U.S. Pat. No. 5,859,613 does. U.S. Pat. No. 5,859,613 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. Nos. 5,982,808 and 6,600,774 both entitled “SYSTEM AND METHOD FOR COMMUNICATING WITH PLURAL REMOTE TRANSMITTERS,” disclose identifying a plurality of cooperative transmitters by encoding information in a time shifted chirp signal. The present invention does not seek to identify cooperative transmitters, and is directed at identifying uncooperative transmitters. U.S. Pat. Nos. 5,982,808 and 6,600,774 are hereby incorporated by reference into the specification of the present invention.
There exists a need to identify unknown transmitters that have an unknown location and are not cooperative with a receiving station without using expensive TDOA circuitry at each receiving station.